Combustion engines such as diesel engines, gasoline engines, and gaseous-fuel-powered engines burn a mixture of air and fuel within the engine, generating mechanical power and a consequent flow of exhaust. Engine exhaust contains, among other things, unburnt fuel, particulate matter such as soot, and harmful gases such as nitrous oxide or carbon monoxide. Modern engines must meet stringent emissions standards, which permit engines to discharge only miniscule levels of nitrous oxide and soot into the atmosphere. To comply with these standards, modern engines often use an exhaust gas recirculation (EGR) system, which recirculates a portion of the exhaust through the combustion chambers, which is known to reduce undesirable emissions at the engine outlet.
The recirculated exhaust is often cooled in an EGR cooler and mixed with fresh intake air before supplying the mixture to the combustion chambers of the engine. Soot in the recirculated exhaust can, however, foul components of the EGR cooler making it less efficient. The soot in the recirculated exhaust can also damage other components in the engine. Modern engines often incorporate a particulate filter in the EGR system to trap the soot in the recirculated exhaust. Over time, the trapped soot in the particulate filter may block the flow of exhaust in the EGR system, reducing its effectiveness.
One attempt to address the problems described above is disclosed in U.S. Pat. No. 5,671,600 of Pischinger et al. that issued on Sep. 30, 1997 (“the '600 patent”). The '600 patent discloses a turbocharged diesel engine. A portion of the exhaust flowing to the turbocharger is branched off, passed through a particulate filter and reintroduced into the charge air upstream of the compressor. The '600 patent also discloses an oxidizing catalyst coupled with the particulate filter for regeneration of the particulate filter. The '600 patent discloses that the filter has small dimensions, which allow the filter to heat up quickly for regeneration when the engine is driven in the full load range.
Although the system of the '600 patent may be able to regenerate the filter in the EGR loop by oxidizing the soot trapped in the particulate filter in the presence of a catalyst, the system may still be less than optimal. For example, the system of the '600 patent relies on the small dimensions of the filter to enable the filter to heat up quickly. A small filter, however, may not be suitable for filtering soot in the EGR systems in large engines. Moreover, the system of the '600 patent may not be able to regenerate the filter when the engine operates at relatively low loads for an extended period of time.
The engine system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.